1. Field of the Invention
The present invention relates to a magnetoresistive element used for a magnetic head and the like, and more particularly, the invention relates to a magnetoresistive element utilizing a spin-valve effect and to a method of making the same.
2. Description of the Related Art
Magnetoresistive elements are increasingly used for magnetic heads in magnetic disk units and the like because of their high magnetic field sensitivity. FIG. 8 is a sectional view of a magnetic core of a magnetic head using a conventional magnetoresistive element, viewed from the surface facing a magnetic disk. A magnetic core 31, which includes a read head 32 and a write head 33, is provided on the trailing end of a slider 34. The magnetic core 31 and the slider 34 constitute a magnetic head 35.
In the read head 32, an underlying layer 36, a lower shielding layer 37, a lower gap layer 38, an underlying layer 39, an antiferromagnetic layer 40, a first ferromagnetic layer 41, a nonmagnetic conductive layer 42, and a second ferromagnetic layer 43 are deposited in that order on the trailing end of the slider 34, and a pair of bias layers 44 are placed on both sides of the second ferromagnetic layer 43 with a distance corresponding to a track width T of the magnetic disk therebetween. An electrode layer 45 is formed on each bias layer 44, and an upper gap layer 46 is deposited so as to cover the electrode layers 45 and the second ferromagnetic layer 43 located therebetween. An upper shielding layer 47 which also acts as a lower core layer of the write head 33 is deposited on the upper gap layer 46.
In the write head 33, a gap layer 48 is formed on the lower core layer 47, and an upper core layer 49 is formed thereon.
The antiferromagnetic layer 40, the first ferromagnetic layer 41, the nonmagnetic conductive layer 42, the second ferromagnetic layer 43, the pair of bias layers 44, and the pair of electrode layers 45 constitute a magnetoresistive element 50.
The first ferromagnetic layer 41 is composed of, for example, a Co film, an NiFe alloy, a CoNiFe alloy, a CoFe alloy, or a CoNi alloy. The antiferromagnetic layer 40 is composed of a PtMn alloy or the like. The bias layers 44 are composed of a conductive antiferromagnetic material, such as an IrMn alloy or an FeMn alloy.
The first ferromagnetic layer 41 shown in FIG. 8 is magnetized by an exchange anisotropic magnetic field due to exchange coupling occurring at the interface with the antiferromagnetic layer 40, and the antiferromagnetic layer 40 and the first ferromagnetic layer 41 are magnetically coupled to each other. The magnetization direction of the first ferromagnetic layer 41 is fixed in the Y direction in the drawing, i.e., in the direction crossing to the magnetic disk (in the height direction) by the coupling.
The second ferromagnetic layer 43 is magnetized by an exchange anisotropic magnetic field of the pair of bias layers 44, is magnetically coupled to the pair of bias layers 44 in regions in which the second ferromagnetic layer 43 is in direct contact with the pair of bias layers 44, and is aligned in a single-domain state as a whole. The magnetization direction of the second ferromagnetic layer 43 is aligned in the direction opposite to the X1 direction in the drawing, i.e., in the direction crossing to the magnetization direction of the first ferromagnetic layer 41. Due to the single-domain state, in the regions in which the second ferromagnetic film 43 and the pair of bias layers 44 are in direct contact with each other, the magnetization direction of the second ferromagnetic layer 43 is fixed in the direction opposite to the X1 direction in the drawing, and domain walls are inhibited from appearing in the second ferromagnetic layer 43, and thus Barkhausen noise is prevented from occurring.
In the magnetoresistive element 50, a sensing current (steady-state current) is applied from the electrode layer 45 to the second ferromagnetic layer 43, the nonmagnetic conductive layer 42, and the first ferromagnetic layer 41, and when a fringing magnetic field from a magnetic disk which rotates and travels in the Z direction is applied in the Y direction in the drawing, the magnetization direction of a portion of the second ferromagnetic layer 43 which is not in direct contact with the pair of bias layers 44 changes from the direction opposite to the X1 direction in the drawing to the Y direction. Because of the relationship between the change in the magnetization direction in the second ferromagnetic layer 43 and the magnetization direction of the first ferromagnetic layer 41, the electrical resistance changes, and the fringing magnetic field from the magnetic disk is detected by a voltage change based on the change in the electrical resistance.
In order to fabricate the magnetoresistive element 50 shown in FIG. 8, as shown in FIG. 9, the individual layers from the antiferromagnetic layer 40 to the second ferromagnetic layer 43 are formed in a vacuum, and by performing heat treatment (annealing) in a magnetic field, an exchange anisotropic magnetic field is produced at the interface between the first ferromagnetic layer 41 and the antiferromagnetic layer 40, and the magnetization direction of the first ferromagnetic layer 41 is fixed in the Y direction in the drawing. The above structure is then taken out into air, and a lift-off resist layer 51 having a width substantially corresponding to the track width T is formed as shown in FIG. 10. Next, as shown in FIG. 11, the bias layer 44 and the electrode layer 45 are formed on the surface of the second ferromagnetic layer 43 including the lift-off resist layer 51, and then the lift-off resist layer 51 is removed, and by aligning the magnetization direction of the second ferromagnetic layer 43 in the track width direction, the magnetoresistive element 50 shown in FIG. 8 is obtained.
However, in the conventional magnetoresistive element 50 described above, in order to form the lift-off resist layer 51 shown in FIG. 10, after the individual layers from the antiferromagnetic layer 40 to the second ferromagnetic layer 43 are formed in a vacuum and the magnetization direction of the first ferromagnetic layer 41 is fixed in the Y direction by performing heat treatment in a magnetic field, the structure must be taken out into air. Consequently, the surface of the second ferromagnetic layer 43 is brought into contact with air, and foreign matter, such as dust in air and contamination, adheres to the surface. As a result, it is not possible to sufficiently bring the second ferromagnetic layer 43 and the pair of-bias layers 44 into close contact with each other, and magnetic coupling between the second ferromagnetic layer 43 and the pair of bias layers 44 becomes insufficient, resulting in the occurrence of domain walls. Thereby, it is not possible to avoid Barkhausen noise which is caused by irregular movement of domain walls.
Accordingly, it is an object of the present invention to provide a magnetoresistive element and a method of making the same in which a second ferromagnetic layer and a bias layer can be magnetically coupled to each other satisfactorily, and Barkhausen noise can be prevented from occurring.
In accordance with one aspect of the present invention, a magnetoresistive element includes a nonmagnetic conductive layer, first and second ferromagnetic layers which are conductive and which sandwich the nonmagnetic conductive layer, an antiferromagnetic layer magnetically coupled to the first ferromagnetic layer for fixing the magnetization direction of the first ferromagnetic layer, a bias layer magnetically coupled to the second ferromagnetic layer for aligning the magnetization direction of the second ferromagnetic layer in a direction crossing to the magnetization direction of the first ferromagnetic layer, and a pair of electrode layers for applying a sensing current to the first and second ferromagnetic layers and the nonmagnetic conductive layer. The antiferromagnetic layer, the first ferromagnetic layer, the nonmagnetic conductive layer, the second ferromagnetic layer, and the bias layer are deposited in that order. The pair of electrode layers are disposed on both ends of the bias layer, and the bias layer located between the pair of electrode layers is modified to form a nonmagnetic layer for determining a track width.
Preferably, the thickness of the nonmagnetic layer is set smaller than that of the bias layer disposed on either side of the nonmagnetic layer.
Preferably, the bias layer is composed of an antiferromagnetic material.
Preferably, the nonmagnetic layer is composed of a mixture in which at least one element selected from the group consisting of oxygen, nitrogen, and boron is mixed with the antiferromagnetic material.
Preferably, the bias layer is composed of an Xxe2x80x94Mn alloy, where X is at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir, and Os.
In accordance with another aspect of the present invention, in a method of fabricating a magnetoresistive element including a laminate which includes a nonmagnetic conductive layer, first and second ferromagnetic layers which are conductive and which sandwich the nonmagnetic conductive layer, an antiferromagnetic layer magnetically coupled to the first ferromagnetic layer for fixing the magnetization direction of the first ferromagnetic layer, and a bias layer magnetically coupled to the second ferromagnetic layer for aligning the magnetization direction of the second ferromagnetic layer in a direction crossing to the magnetization direction of the first ferromagnetic layer, the method includes the steps of forming the laminate by depositing the antiferromagnetic layer, the first ferromagnetic layer, the nonmagnetic conductive layer, the second ferromagnetic layer, and the bias layer in that order; forming a pair of electrode layers for applying a sensing current to the first and second ferromagnetic layers and the nonmagnetic conductive layer on the bias layer with a distance corresponding to a track width therebetween; and modifying the bias layer located between the pair of electrode layers by plasma treatment to form a nonmagnetic layer.